1. Field of the Invention
This invention relates to fertilizers and fertilizer dispensers, and more particularly to apparatus and methods for delivering beneficial agents, such as fertilizers, to subterranean locations.
2. Background
Today's gardeners are offered an immense array of choices when it comes to fertilizer products. While no fertilizer is perfect for every garden or situation, slow- and controlled-release fertilizers offer some important advantages over other fertilizer products. These fertilizers release nutrients over a relatively long period of time, rather than over a brief period as occurs with many liquid, powder, or granular fertilizers currently on the market. In general, slow-release fertilizers may release nutrients at a slow but unpredictable rate. In certain cases, the release rate may depend on the activity of organisms, the size of the fertilizer granules, or the amount of water in the soil. Controlled-release (often referred to as “coated”) fertilizers, on the other hand, may release their nutrients at a more predicable rate over a period of time.
Both the slow- and controlled-release fertilizers may reduce the “feast-or-famine” effect that occurs when fast-release fertilizers are used. Using fast-release fertilizers, an abundance of nutrients may briefly surround the roots of a plant soon after application. These nutrients may be rapidly washed away or consumed, however, allowing nutrient deficiencies to occur. Furthermore, fast-release fertilizers may easily be applied in excess, potentially damaging the plants they are intended to nourish. Because slow- and controlled-release fertilizers release their nutrients gradually over time, each of the above problems may be reduced or minimized.
Environmental concerns provide yet another reason to use slow- and controlled-release fertilizers. In some areas of the country, fertilizers significantly contribute to waterway, stream, and groundwater pollution. Because slow- and controlled-release fertilizers release their nutrients over time, these fertilizers are less likely to be found in the amounts and concentrations needed to contribute to these types of pollution.
Although slow- and controlled-release fertilizers provide various advantages, they are not without shortcomings. For example, the water-solubility of many fertilizers may cause them to dissolve and leach into the soil below the roots, thereby never becoming available to the plants there are intended to nourish. Temperature may also undesirably affect fertilizer release rates. For example, in controlled-release fertilizers, temperature may affect nutrient diffusion across the coating. In slow-release fertilizers, temperature may exert a major influence on microbial activity, affecting the release of nutrients. In other cases, fertilizer granule or particle size may change as the fertilizer dissolves. This may affect the fertilizer particle or granule surface area and thus the release rate into the soil.
Furthermore, fertilizer granules or powders are frequently non-uniform in size and composition. Granules in particular may contain cracks and therefore tend to pulverize easily. The result is that it is often difficult to obtain a uniform and practical coating for many granular fertilizers. Furthermore, potential uses for a fertilizer may be difficult to anticipate at the time the fertilizer is manufactured. Thus, a particular coating and granular size, while appropriate for some applications, may be unlikely to provide desirable results in other applications.
In view of the foregoing, what are needed are apparatus and methods for delivering beneficial agents, such as fertilizers, including “fast-release” fertilizers, to subterranean locations in a controlled, predictable manner. Ideally, such an apparatus and method would be suitable to disperse a wide variety of different fertilizer products. Further needed are apparatus and methods for easily controlling the rate at which the beneficial agents are released into the soil.